Play area is defined as: ... the shared space occupied by ships, squadrons, obstacle tokens and objective tokens. It's 3x3 for Core set, or 3x6 for 300-400 pt games.
Share is defined as:
A
part
or
portion
belonging
to,
distributed
to,
contributed
by,
or
owed
by
a
person
or
group.
Occupy is defined as:
To
fill
up
(time
or
space),
To
dwell
or
reside
in.
"If any portion of a ship’s or squadron’s base is outside the play area, that ship or squadron is destroyed. For this purpose, ignore activation sliders, shield dials, and the plastic portions of a ship’s base that frame shield dials."
You must deploy ships to the play area, specifically the deployment area, a subset of the setup area, which is a part of the play area.
Lyraeus' question posits that nothing prevents you from deploying your ships on top of each other, as "overlapping" is only directly addressed as happening after movement. The main problem with this interpretation is that because of how play area is defined, that would mean that everything on the play area
becomes
the play area as well, and you'd never be able to "go off" the play area. Ships could hang off the edge, and that'd be okay,
because now they're part of the play area by extension.
That's a direct violation of the entire purpose of the second paragraph under Play Area on pg. 9 of the Rules Reference. Sharing and occupy only means that the ships, squadrons, obstacles and objective tokens get to use that space on the play area. They do not become part of the play area itself.
The play area is the surface the game is played upon. Ships
share
that space, but do not
become
part of the play area. You must deploy onto the play area. Therefore you never gain the opportunity to deploy your ship/squadron on top of another ship or squadron because that is not a valid deployment location.